Method and arrangement for establishing a communication session for multimedia

ABSTRACT

A method and arrangement for establishing a packet-switched multimedia session for a mobile terminal connected to a mobile access network. A first Radio Access Bearer RAB is obtained, and the multimedia session is started by communicating media over the first RAB. Simultaneously with the media communication, a quality of communicated media is monitored and evaluated. If the monitored quality is deemed unacceptable, a media-adapted second RAB is obtained, and the session is continued over the second RAB. Thereby, it is not necessary to delay the communication of media by waiting for the second RAB to be obtained.

TECHNICAL FIELD

The present invention relates generally to a method and arrangement forestablishing a communication session for multimedia involving a mobileterminal. In particular, the invention may reduce the delay before themobile terminal can start communicate media.

BACKGROUND

With the emergence of 3G mobile telephony, new packet-basedcommunication technologies have been developed to support multimediacommunication. For example, GPRS (General Packet Radio Service) andWCDMA (Wideband Code Division Multiple Access) technologies supportwireless multimedia telephony services involving packet-switchedcommunication of data representing images, text, documents, animations,audio files, video files, etc., in addition to traditionalcircuit-switched voice calls.

Multimedia services typically entail transmission of encoded datarepresenting text, documents, images, audio files and video files indifferent formats and combinations. The term “multimedia” will be usedin this description as generally referring to any choice of mediacommunicated by using the packet based IP (Internet Protocol) transporttechnology.

A network architecture called “IP Multimedia Subsystem” (IMS) has beendeveloped by the 3^(rd) Generation Partnership Project (3GPP) as an openstandard for handling multimedia services and sessions in the packetdomain. IMS is a platform for enabling services based on IP transport,more or less independent of the access technology used, and is neitherrestricted to any specific services. Thus, IMS networks are used forcontrolling multimedia sessions by acting as a “control plane” for thesessions, whereas the actual transfer of payload data is typicallyrouted over access networks and any intermediate transport networks,although nodes in the IMS network may also be used.

FIG. 1 is a simplified schematic illustration of a basic networkstructure for providing multimedia services by means of an IMS servicenetwork. A first mobile terminal A is connected to a first radio accessnetwork 100 and communicates with a second mobile terminal B connectedto a second radio access network 102, in a communication session Sinvolving one or more multimedia services. There may also be anintermediate backbone network, not shown, as well linking the accessnetworks 100 and 102.

An IMS network 104 is connected to the first radio access network 100and handles the session with respect to terminal A. In this figure, acorresponding IMS network 106 handles the session on behalf of terminalB, and the two IMS networks 104 and 106 may be controlled by differentoperators. Alternatively, terminals A and B may of course be connectedto the same access network and/or may belong to the same IMS network.Terminal A may also communicate with a fixed terminal or computer orserver instead, e.g. for downloading some media over the Internet, aslong as the other party is capable of SIP communication. Moreover, if aterminal is roaming in a visited access network, multimedia services arehandled by the terminal's “home” IMS network.

The session S shown in FIG. 1 is managed by specific nodes in each IMSnetwork, here generally referred to as “session managing nodes” 108.These nodes typically include S-CSCF (Serving Call Session ControlFunction), I-CSCF (Interrogating Call Session Control Function) andP-CSCF (Proxy Call Session Control Function). Each IMS network 104,106also includes one or more application servers 110 for enabling variousmultimedia services. Further, a main database element HSS (HomeSubscriber Server) 112 stores subscriber and authentication data as wellas service information, among other things. IMS network 106 is basicallysimilar to network 104. The various specific functions of the shownnetwork elements 108-112 are generally known in the art, but are notnecessary to describe here further to understand the context of thepresent invention. Of course, the IMS networks 104,106 contain numerousother nodes and functions not shown here for the sake of simplicity.

A specification for handling sessions in IMS networks has been definedcalled “SIP” (Session Initiation Protocol, according to the standardIETF RFC 3261). SIP is an application-layer control protocol forsignalling, to create and generally handle sessions over apacket-switched logic. The SIP standard is thus used by IMS systems andSIP-enabled terminals to establish and control IP multimediacommunications. SIP itself does not provide multimedia services, butrather makes available a set of primitives that other protocols orapplications can use to actually implement such services. For example, amessage called “INVITE” is defined in SIP to initiate multimediasessions. The SIP INVITE message includes, among other things,information on what application server to invoke during session set-up,a nickname and SIP URI (Universal Resource Identifier) of the callingparty, the SIP URI of the called party, and other communicationparameters needed for the forthcoming session.

SIP uses an additional protocol called Session Description Protocol,SDP, for describing the media content to be transferred in multimediasessions. An SDP message can be embedded as a self-contained body withinSIP messages. SDP messages can be used by terminals to exchangeinformation regarding their specific capabilities and preferences, inorder to negotiate and agree on which session parameters, codecs inparticular, to use during a forthcoming multimedia session, as iswell-known in the art.

Many mobile applications require a certain Quality of Service QoS inorder to provide a satisfying result to end-users. For UMTS networks,four main QoS traffic classes have been defined: “conversational class”,“streaming class”, “interactive class” and “background class”, in orderto classify different needs regarding bitrates and delays. These classesare primarily distinguished by their requirements regarding transferdelays, such that applications of the conversational class tolerate onlysmall delays, sometimes also referred to as “real-time”, whereas thebackground class is applied to the least delay-sensitive applications,sometimes also referred to as “best effort”.

The selection of a UMTS QoS traffic class for an application is used forassigning a suitable Radio Access Bearer RAB in the access network,including a radio channel, in order to optimise the scarce radiorecourses in the access network whilst maintaining acceptable qualityfor the end-user.

Mobile terminals capable of multimedia are typically configured toidentify for each inherent application, a UMTS QoS traffic class, asschematically illustrated in FIG. 2. Thus, a mobile terminal may hold anumber of applications 200, denoted as A1, A2, A3, A4, A5 . . . . Amapping function 202 in the terminal translates each application to acertain UMTS QoS traffic class 204, of which only two are shown here. Inthis case, applications A1, A2 and A4 are mapped to the same UMTS QoStraffic class 2, since they have similar requirements regarding bitrateand delay, whereas applications A3 and A5 are mapped to UMTS QoS trafficclass 1. In this way, several applications with similar characteristicsmay be mapped onto the same RAB, fulfilling their requirements.

However, before a mobile terminal can exchange any SIP messages with theIMS network, a “PDP context” must be established for the terminal.Basically, a PDP context can be activated once the terminal has beenpowered on. Activating a PDP context for a mobile terminal includesallocating an IP address to the terminal, to be able to communicate datapackets with the terminal. A PDP context also means that an RAB isallocated in the access network for IP communication. Thus, SIP messagescan only be sent over a PDP context.

FIG. 3 illustrates the gradual activation of a mobile terminal A aboutto communicate multimedia with another party, involving basically fivestages 3:1-3:5 as illustrated, each comprising various messages back andforth. These messages are well-known in the art and will not bedescribed in any detail. Terminal A is located under radio coverage of amobile access network 300, which is divided into a radio network part300 a and a core network part 300 b including the nodes SGSN (ServingGPRS Switching Node), HLR (Home Location Register) and GGSN (GatewayGPRS Switching Node), among other things. The other party may be anothermobile terminal B connected to a mobile access network 302, or a fixedtelephone or computer, or a server connected to the Internet 304.

In a first stage 3:1, when terminal A is powered on, it is registered asa connected “Mobile Station MS” with the access network 300, forcircuit-switched communication. SGSN and HLR in core network 300 b areinvolved in this initial stage of establishing a radio connection forattaching the terminal.

Next, a first PDP context, referred to as “primary”, is activated in astage 3:2, to obtain an IP connection. Activating the primary PDPcontext includes obtaining a RAB for packet-switched SIP signallingmessages over IP. The PDP context is created by GGSN in network 300 b.This RAB is typically based on so-called “best effort” communicationwith no particular requirements regarding bitrate and delay, since it isonly intended to occasionally carry relatively short SIP messages.Furthermore, the RAB characteristics of a primary PDP context mayfluctuate depending on variations in available capacity and bandwidth inthe access network. “Best effort” means basically that any availableradio resources and bandwidth not needed for other connections withhigher priority, can be used. Thus, the primary PDP context is adaptedfor signalling messages.

In a third stage 3:3, terminal A registers with the IMS network 306, asbasically handled by an S-CSCF node and HSS therein, as illustrated. TheIMS registration involves a certain amount of SIP-based signalling overthe primary PDP context.

Next, a multimedia session is to be established with another party in afollowing stage 3:4. In this stage, the above-mentioned protocol SDP isused within the SIP messages, such as INVITE, to communicatesession-specific parameters including codecs. The following UMTSparameters may be derived from the SDP message: Traffic class, Maximumbitrate (uplink/downlink), Guaranteed bitrate (uplink/downlink),Transfer delay (uplink/downlink), Delivery order, Maximum SDU (ServiceData Unit) size and a Source Statistic Descriptor.

In a next stage 3:5, a secondary PDP context is activated for terminalA, and should be adapted for the media type(s) involved in theforthcoming session. The secondary PDP context is handled by GGSN in thesame manner as for the primary PDP context in stage 3:2. Thus, thesecondary PDP context should be defined so as to fulfil the requirementsof the session with respect to the SDP information as well as otherfactors, in order to obtain a proper RAB for media to be communicated.The new RAB is thus more stable and reliable as compared to the firstone associated with the primary PDP context.

Activating the secondary PDP context according to stage 3:5 is asomewhat time-consuming process. It should be noted that, if the otherparty is an IMS enabled mobile terminal B, a corresponding process takesplace on the other side for that terminal as well. When the secondaryPDP context has finally been activated, the session can start asillustrated in a stage 3:6, using the allocated new RAB.

The communication of media is thus delayed by waiting for the secondaryPDP context to be activated and a corresponding RAB to be allocated,according to conventional set-up procedures for multimedia sessions. Inthe field of mobile communication, it is generally desirable to minimisesuch delays in order to make multimedia services more attractive tomobile end-users. It is also desirable to reduce the complexity andgeneral amount of signalling in the session set-up procedure. In mobilenetworks, it is further generally desirable to avoid excessiveoccupation of bandwidth in the air interface due to scarce radioresources.

SUMMARY

It is an object of the present invention to address at least some of theproblems outlined above. More specifically, it is an object of thepresent invention to make it possible to reduce delays and bandwidthoccupation when mobile terminals communicate media.

These objects and others can be obtained by providing a method and amobile terminal according to the independent claims attached below.

In the inventive method of establishing a packet-switched multimediasession for a mobile terminal connected to a mobile access network forthe communication of media, a first Radio Access Bearer RAB is obtained,and the multimedia session is started by communicating the media overthe first RAB. A quality of communicated media is monitored andevaluated simultaneously with the media communication over the firstRAB. If the monitored quality is deemed unacceptable, a media-adaptedsecond RAB is obtained based on quality requirements of the ongoingmedia communication, and the session continues over the second RAB.

The first RAB may be obtained by activating a primary PDP contextadapted for signalling messages or by activating a pre-establishedsecondary PDP context adapted for media communication. The first RAB mayfurther be a default RAB. Alternatively, the first RAB may be adaptedfor said communicated media, initially. The session may be completedover the first RAB, if the monitored quality remains acceptablethroughout the session.

The media-adapted second RAB may be obtained by activating a secondaryPDP context adapted for said communicated media, or by modifying thefirst RAB and pre-established secondary PDP context to be adapted forsaid communicated media. The communication of media is then switchedfrom the first RAB to the media-adapted second RAB, once the secondaryPDP context has been activated or the pre-established secondary PDPcontext has been modified.

The media-adapted second RAB may be obtained when at least one mediastream has been added or changed during the ongoing media communication.

The quality may be monitored according to a predetermined monitoringalgorithm. The quality of a received media stream can be monitored bymeasuring any of the following parameters: a packet buffer size in theterminal, a transfer bitrate, a bit error rate, a retransmission rate,and detected disturbances in the play-out or presentation of media to anend-user, as input to said monitoring algorithm. The monitoringalgorithm may be configured such that the monitored quality is deemedacceptable as long as the measured buffer size stays above apredetermined level, and/or if the measured bitrate of the media streamstays above a predetermined level, and/or if the measured bit error rateand/or retransmission rate does not exceed a predetermined level. Themonitoring algorithm may further be configured such that the monitoredquality is deemed unacceptable whenever one or more of the measuredparameters stays above or does not exceed, respectively, said level(s)for a preset duration or repeatedly.

If SIP is used for signalling, the monitoring algorithm may be based onrequirements derived from information in an SDP message given in anINVITE message, and/or a response thereto.

The quality of communicated media may be monitored and evaluated by themobile terminal. Alternatively or additionally, the quality may furtherbe monitored and evaluated by a quality monitor in the mobile accessnetwork or in a multimedia service network currently controlling thesession. Obtaining a media-adapted second RAB may be initiated bysending a PDP context triggering message to the mobile terminal or to aGGSN node in the mobile access network.

The present invention further provides an arrangement for establishing apacket-switched multimedia session for a mobile terminal connected to amobile access network for the communication of media. The inventivearrangement comprises means for obtaining a first Radio Access BearerRAB, means for starting the multimedia session by communicating saidmedia over the first RAB, means for monitoring and evaluating a qualityof communicated media simultaneously with the media communication overthe first RAB, and means for obtaining a media-adapted second RAE basedon quality requirements of the ongoing media communication, if themonitored quality is deemed unacceptable. Thereby, the session cancontinue over said second RAB.

The means for obtaining a first RAB may be configured to obtain thefirst RAB by activating a primary PDP context adapted for signallingmessages, or by activating a pre-established secondary PDP contextadapted for media communication. The first RAB may further be a defaultRAB. Alternatively, the first RAB may be initially adapted for saidcommunicated media.

The inventive arrangement may further comprise means for completing thesession over the first RAB, if the monitored quality remains acceptablethroughout the session. Otherwise, the means for obtaining amedia-adapted second RAB may be configured to obtain the second RAB byactivating a secondary PDP context adapted for said communicated media.The means for obtaining a media-adapted second RAB may further beconfigured to obtain the second RAB by modifying said first RAB andpre-established secondary PDP context to be adapted for saidcommunicated media.

The inventive arrangement may further comprise means for switching thecommunicated media from the first RAB to the second RAB, once thesecondary PDP context has been activated or the pre-establishedsecondary PDP context has been modified. The means for obtaining amedia-adapted second RAB may further be configured to obtain amedia-adapted second RAB when at least one media stream has been addedor changed during the ongoing media communication.

The monitoring and evaluating means may be configured to monitor thequality according to a predetermined monitoring algorithm. Themonitoring and evaluating means may further be configured to obtainmeasurements of any of the following parameters: a packet buffer size inthe terminal, a transfer bitrate, a bit error rate, a retransmissionrate, and detected disturbances in the play-out or presentation of mediato an end-user, and to provide said measurements to the processor asinput to said monitoring algorithm to indicate the quality of a receivedmedia stream.

The monitoring algorithm may be configured such that the quality isdeemed acceptable as long as the measured buffer size stays above apredetermined level, and/or if the measured bitrate of the media streamstays above a predetermined level, and/or if the measured bit error rateand/or retransmission rate does not exceed a predetermined level. Themonitoring algorithm may further be configured such that the monitoredquality is deemed unacceptable whenever one or more of the measuredparameters stays above or does not exceed, respectively, said level(s)for a preset duration or repeatedly.

If SIP is used for signalling, the monitoring algorithm may be based onrequirements derived from information in an SDP message given in anINVITE message, and/or a response thereto.

The monitoring and evaluating means is implemented in the mobileterminal, or as a quality monitor in the mobile access network or in amultimedia service network currently controlling the session. The meansfor obtaining a media-adapted second RAB may be configured to send a PDPcontext triggering message to the mobile terminal or to a GGSN node inthe mobile access network.

The present invention further provides an arrangement in a mobileterminal, when connected to a mobile access network, for establishing apacket-switched multimedia session for the communication of media. Theinventive mobile terminal arrangement comprises a communication unitconfigured to obtain a first Radio Access Bearer RAB, and to start themultimedia session by communicating media over the first RAB, and aprocessor configured to monitor and evaluate a quality of communicatedmedia simultaneously with the media communication over the first RAB,and to trigger the communication unit to obtain a media-adapted secondRAB based on quality requirements of the ongoing media communication, ifthe monitored quality is deemed unacceptable. Thereby, the session cancontinue over said second RAB.

The mobile terminal arrangement may further comprise a measuring unitconfigured to provide measurements to the processor from at least oneof: a data buffer, a decoder and a media play-out unit.

The present invention further provides a quality monitor for monitoringand evaluating a quality of communicated media. The inventive qualitymonitor comprises a measurement receiver for receiving qualitymeasurements regarding an ongoing multimedia session for a mobileterminal using a first RAB, a processor for evaluating the qualitymeasurements and for determining whether a media-adapted second RAB isneeded to fulfil quality requirements of the ongoing multimedia session.The quality monitor also comprises and a PDP context triggering unitconfigured to send a message to the mobile terminal or to a GGSN node inthe access network, if said quality is deemed unacceptable, said messagetriggering a media-adapted second RAB based on quality requirements ofthe ongoing media communication. Thereby, the session can continue oversaid second RAB.

The inventive quality monitor may be configured to be implemented in amobile access network to which the mobile terminal is currentlyconnected, or in a multimedia service network currently controlling thesession. The quality monitor may further be configured to receivequality measurements from at least one of: a mobile access network towhich the mobile terminal is currently connected, a multimedia servicenetwork currently controlling the session, and the mobile terminal.

Further features of the present invention and its benefits will beexplained in the detailed description below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail by means ofpreferred embodiments and with reference to the accompanying drawings,in which:

FIG. 1 is a schematic view of a conventional network structure forcommunicating multimedia between two mobile terminals.

FIG. 2 is a schematic diagram illustrating the mapping of applicationsonto UMTS QoS traffic classes in a mobile terminal.

FIG. 3 is a signalling diagram illustrating different stages in theprocess of establishing multimedia communication, according to the priorart.

FIG. 4 is a signalling diagram illustrating different stages in theprocess of establishing multimedia communication for a mobile terminal,in accordance with one embodiment.

FIG. 5 is a flow chart illustrating a procedure for establishingmultimedia communication for a mobile terminal, in accordance withanother embodiment.

FIG. 6 is a schematic block diagram illustrating an arrangement in amobile terminal, in accordance with yet another embodiment.

FIG. 7 is a signalling diagram illustrating different stages in theprocess of establishing multimedia communication for a mobile terminal,in accordance with yet another embodiment.

FIG. 8 is a schematic block diagram illustrating an arrangement in amonitor unit that can be implemented in an access network, a multimediaservice network, or in some node outside the multimedia service network,in accordance with yet another embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

Briefly described, the present invention is directed to starting mediacommunication over a first RAB, and if the quality of communicated mediabecomes unacceptable, a second RAB is obtained based on qualityrequirements of the ongoing media communication. In other words, thesecond RAB is selected to fulfil those quality requirements when notbeing fulfilled by means of the first RAB, and the session is thencontinued on the second RAB.

For example, if the first RAE is obtained by activating a primary PDPcontext adapted for signalling messages, it is not necessary to waituntil a secondary PDP context has been activated before communicatingthe media, at least initially, and delays can thus be reduced. It isalso possible to communicate media over a “pre-established” secondaryPDP context using a default RAB that has not been specifically adaptedto the communicated media, which will be described in more detail laterbelow.

As described above, the concept of a primary PDP context was originallyintended to be used for signalling messages only, e.g. according to SIP,the RAB of a primary PDP context naturally being a default RAB. As aresult, the RAB characteristics of a primary PDP context are typicallynot stable and can vary over time, being based on best effort.Nevertheless, it may well be the case in some situations that theobtained first RAB, e.g. for the primary PDP context, is quite good withrespect to QoS, e.g. when located in a cell currently having much freeradio resources. Therefore, communication of media over a primary PDPcontext may be successful, even if no secondary PDP context according torequirements of the application and media used, has been activated asyet.

A so-called pre-established secondary PDP context is generally intendedto be used for media and can be activated basically at the same time asthe primary PDP context. However, being a pre-established PDP context,its RAB characteristics are determined before the mobile terminal hasany knowledge of the QoS needs for the forthcoming media stream, henceusing a default RAB. Therefore, the default RAB of a pre-established PDPcontext may or may not fulfil the QoS requirements for the media. Thus,the pre-established secondary PDP context can also be considered as“best-effort” type, and its characteristics are typically not stable andmay vary over time. Nevertheless, it may well be the case in somesituations that the obtained first RAB for the pre-established secondaryPDP context is well-suited for the media transfer. Therefore,communication of media over a pre-established secondary PDP context maybe successful as well, at least for a period of time.

In another case, media may be communicated after establishing a“regular” secondary PDP context, as described in the background sectionabove, using a first RAB that has been properly obtained based onquality requirements of the media communication. Still, the quality ofcommunicated media may become unacceptable after a while, e.g. iffurther media is added to the session, or if the radio conditions shoulddeteriorate. By monitoring and evaluating the quality, a second RAB canthen be obtained that fulfils those quality requirements, as soon as thefirst RAB fails to do so.

In order to maintain a proper QoS during a session, even if afluctuating first RAB should deteriorate or further media is added, theactual QoS is thus monitored and evaluated in the background as media iscommunicated over the first RAB. The QoS can be monitored by the mobileterminal or by a network node, as will be illustrated below. Ifmonitored by the mobile terminal, and if the QoS should fall below apredetermined acceptance level, i.e. become unacceptable to an end-user,the mobile terminal may either:

-   -   issue a request for a secondary PDP context towards the access        network, in order to obtain a new RAB that fulfils the QoS        requirements of the application used, or issue a request for a        modification of a pre-established secondary PDP context towards        the access network, in order to obtain, e.g., a guaranteed        higher bit-rate or decreased transfer delays.

In the case when a new RAB has been obtained, one or more media flowsare moved from the previous RAB to the new RAB, for continuedcommunication. Below, three practical examples are given.

Example 1

In the case of a plain voice service, the voice media stream may bemoved from a primary PDP context using a first RAB, to a secondary PDPcontext using a second RAB.

Example 2

In the case of a voice and video service, both the video stream and thevoice stream may be moved to the newly-established PDP context using asecond RAB.

Example 3

In the case of a voice service already running over a pre-establishedsecondary PDP context using a first RAB, in which a video stream isintroduced at some point, a new secondary PDP context, in effect being athird PDP context, may be established using a second RAB. The videostream may be moved to the new (second) RAB of the secondary PDPcontext, while the voice stream is still communicated on the previous(first) RAB.

It should be noted that the end-user may perceive the switch of PDPcontext and RAB as a temporary pause in the play-out of received mediaor a conversation, depending on whether a buffer in the terminal isempty on received data packets or not.

In the case when a pre-established secondary PDP context has beenmodified, the second RAB in this context is a modified first RAB forcontinued communication. For example, a media stream may have started ona pre-established secondary PDP context using a first RAB. If then themonitored QoS falls below a predetermined acceptance level, the secondRAB may be obtained by modifying the PDP context and the first RAB withrespect to the QoS required for the media stream.

On the other hand, if the monitored QoS stays above the acceptance levelthroughout the session using a first RAB, it may not become necessary atall to request for a secondary PDP context, or to modify apre-established secondary PDP context, and switch to a second RAB. Thefirst RAB may thus be used throughout the session, when fulfilling theQoS requirements. In that case, much signalling has been avoided for thesession as compared to the conventional procedure, thereby saving bothtime and bandwidth. Moreover, the initially obtained first RAB may notdemand as much radio resources as a second RAB would do. When the firstRAB is obtained for a primary PDP context, the communication of mediacan start over the primary PDP context, i.e. earlier in the process ascompared to the conventional technique described in the backgroundsection. If a secondary PDP context becomes necessary at some pointduring the session, the only nuisance might be a perceived disturbance,if any, of media play-out or in a conversation at the receiving party.

FIG. 4 is a signalling diagram illustrating different stages in theprocess of initiating and controlling multimedia communication,according to one embodiment. In this case, the quality of communicatedmedia is monitored and evaluated in a mobile terminal A. The scenario issimilar to the one shown in FIG. 3, and the same numerals are used forcorresponding elements involved in the session set-up process. It shouldbe noted that the opposite party 400 is generally represented by a block“B/S”, indicating that it may be a mobile or fixed terminal B, acomputer or a server S.

The first three stages of registering the terminal A as a mobilestation, stage 4:1, activating a primary PDP context, stage 4:2, andregistering terminal A in the IMS network, stage 4:3, are basically thesame as stages 3:1, 3:2 and 3:3 in FIG. 3, which will therefore not bedescribed again here. However, stage 4:2 may further include activationof a pre-established secondary PDP context, as mentioned above.

Next, a multimedia session is to be established with opposite party 400,either by terminal A calling or contacting party 400, or vice versa.However, a “quick” session establishment stage 4:4 may now beintroduced, replacing the previous conventional session establishmentstage 3:4 and omitting the stage 3:5 of selection and activation of amedia-adapted secondary PDP context at this point. This may reduce thedelay or waiting time considerably before media transmission can begin,in some cases approximately 1-2 seconds, by omitting all messages backand forth needed for activation of the media-adapted secondary PDPcontext. Hence the epithet “quick”. However, the present invention doesnot exclude establishment of a “regular” secondary PDP context afterstage 4:4, that is based on quality requirements of the mediacommunication.

In the session establishment stage 4:4, the two parties A and B/S maynegotiate and agree on session-specific parameters to be used in theforthcoming session, including codecs, by exchanging suitable SIPmessages, typically an INVITE message and a response message thereto.Moreover, information from an SDP message given in the INVITE message,and/or a response thereto, is also saved for later use, see below.

After establishing the session with the opposite party 400, thecommunication of media is started over the primary (or secondary) PDPcontext using a first RAB, as indicated in a next stage 4:5, assumingthat the first RAB may be capable of conveying the media, at leastinitially, even though it may, e.g., only have been adapted forsignalling messages. Alternatively, the media communication may bestarted over a pre-established or regular secondary PDP-context at thispoint, as described above. The RAB of a pre-established or regularsecondary PDP context will also be referred to as a first RAB in thefollowing. It should be noted that the described procedure may be validfor media transfer in either direction, i.e. to or from terminal A.

The QoS is now simultaneously monitored in the background, as indicatedby a stage 4:6, during the ongoing media communication in stage 4:5. Inparticular, the first RAB may fluctuate and be “unreliable”, typicallywhen obtained as a default RAB for the primary PDP context or for apre-established secondary PDP context. Also, if further media is addedto the session, the QoS requirements would surely change.

The QoS is preferably monitored according to a predetermined monitoringalgorithm, based on requirements derived from the SDP information savedin stage 4:4, as well as other factors related to the communicated mediaand the application(s) used. For example, the QoS of a received mediastream may be monitored and evaluated by measuring any of: the number ofpackets in a buffer in the terminal, the bitrate of the media stream, abit error rate in received packets, the occurrence of retransmissions,errors in the play-out of the media, etc. In short, basically anyparameter that may affect the quality as perceived by end-users.

The monitoring algorithm may be configured in several different ways,and may contain various conditions for evaluating the QoS, e.g.depending on the SDP information, although the present invention is notlimited in this respect. For example, the QoS may be deemed acceptableas long as a measured buffer size stays above a certain level, and/or ifa measured bitrate of the media stream stays above a certain level,and/or if a measured bit error rate or retransmission rate does notexceed a certain level, etc. Further, the monitored QoS may be deemedunacceptable whenever one or more of the above parameters stays above ordoes not exceed, respectively, said level(s) for a preset duration, orrepeatedly, etc. Detected disturbances may further be measured in amedia play-out unit or the like, when presenting received media to theend-user. The monitoring algorithm may be configured to deem the QoSunacceptable if such disturbances exceed a certain level, etc.

If the above measurements generally indicate that the monitored QoSsomehow falls below an acceptable level, a following stage 4:7 ofactivating a secondary PDP context is executed, in order to regainacceptable QoS and a reliable media-adapted (second) RAB fulfillingrequirements of the communicated media. These requirements can be partlyderived from the SDP message given during the session establishmentstage 4:4, as mentioned above. As mentioned above, decreased QoS inrelation to requirements may be the result of a fluctuating best-effortRAB, deteriorated radio conditions or added media.

Stage 4:7 may be initiated as the terminal A sends a PDP context requestto GGSN in the access network. Activating the secondary PDP context isbasically similar to the activation of the primary PDP context. If afirst RAB of a pre-established or regular secondary PDP context was usedfor media transfer in stage 4:5, a new secondary PDP context with asecond RAB adapted for the ongoing media communication, is activated instage 4:7, or the pre-established or regular secondary PDP context andits first RAB may be modified, as described above.

Once the secondary PDP context has been activated and a (new ormodified) second RAB has been allocated that fulfils the specificrequirements of the communicated media, the session basically switchesto the second RAB in a stage 4:8. From now on, the media session iscontinued on the second RAB over the secondary PDP context, in a finalillustrated stage 4:9. The session can now be completed since the newRAB of the secondary PDP context, or modified RAB in the case of amodified pre-established or regular secondary PDP context, has beenadapted to the media and application used, and will be more or less“safe” with respect to any requirements of delay, bitrate and error rateimposed by the media type.

FIG. 5 is a flow chart illustrating an exemplary procedure forcontrolling multimedia communication for a mobile terminal currentlyconnected to a mobile access network, in accordance with one aspect ofthe present invention. The process shown in FIG. 5 may be applied whenthe quality is monitored either by the terminal or the network, and inthe former case it may basically follow the example described above forFIG. 4 when the following steps would be taken by the mobile terminal A.

In a first step 500, e.g. corresponding to stage 4:2, a first RAB isobtained by activating either a primary PDP context basically adaptedfor communication of signalling messages, or a pre-established orregular secondary PDP context for media, e.g. in addition to a primaryPDP context for signalling, as described above. In practice, theterminal may initiate activation of a primary PDP context or apre-established or regular secondary PDP context by sending a PDPcontext request to the access network.

In a next step 502, an application is invoked and a session isestablished with an opposite party, e.g. corresponding to stage 4:4. Thesession may be established according to the “quick” establishment ofomitting activation of a secondary PDP context adapted for the media tobe communicated, or after activating a regular secondary PDP contextaccording to conventional procedures. In practice, the terminal mayinitiate establishment of the session by sending/receiving an INVITEmessage or similar to/from the opposite party.

In a next step 504, media is communicated (received or transmitted orboth) using the first RAB obtained in step 500 for the primary PDPcontext, or for the pre-established or regular secondary PDP context,e.g. corresponding to stage 4:5. In a parallel step 506, the quality, orQoS, of the media communication is monitored, e.g. corresponding tostage 4:6. As indicated in the figure, step 506 is performed in thebackground simultaneously with step 504. The quality of received mediamay be evaluated, e.g., as suggested for stage 4:6 above. The quality oftransmitted media may be evaluated at least by measuring a transmittedbitrate, e.g. in relation to the service description in an SDP message,the quality naturally being dependent on the capacity of the obtainedfirst RAB.

In a next step 508, it is determined whether the monitored quality isacceptable, i.e. if a predetermined quality condition is fulfilledaccording to a suitable predetermined monitoring algorithm, e.g. asdescribed above for stage 4:6. If the monitored quality is deemedacceptable in step 508, the session can continue over the first RAB ofthe primary PDP context or the pre-established or regular secondary PDPcontext, thus repeating steps 504 and 506.

However, if the monitored quality is deemed unacceptable in step 508,according to the used monitoring algorithm, it becomes necessary to moveon to a step 510 of obtaining a better, e.g. more reliable, RAB byactivating a secondary PDP context or by modifying a used first RAB of apre-established or regular secondary PDP context, corresponding to stage4:7. Once activated, the communicated media is moved from the first RABto the second RAB of the newly-activated secondary PDP context, in anext step 512, e.g. basically corresponding to stage 4:8. In thiscontext, the first RAB of a pre-established or regular secondary PDPcontext may be modified into a media-adapted second RAB.

The session can then continue over the second RAB of the newly-activatedsecondary PDP context, in a final illustrated step 514 corresponding tostage 4:9. It should be noted that the terminal may well complete thesession using the first RAB throughout if the monitored quality remainsacceptable, thereby omitting steps 510-514.

An exemplary embodiment of a mobile terminal arrangement, in accordancewith another aspect of the present invention, will now be described withreference to a schematic block diagram shown in FIG. 6. A mobileterminal 600 comprises a communication unit 602 having conventionalelements (not specifically shown here for the sake of simplicity) neededfor transmitting and receiving radio signals over an antenna.Communication unit 602 is connected to a data buffer 604 adapted toaccommodate a queue of data packets of a media stream waiting to bedecoded by a decoder 606, or to be transmitted by the communication unit602, depending on the stream direction. In the shown example, the arrowsin the figure are generally directed for reception of a media stream.

The mobile terminal 600 further includes a “media play-out unit” 608adapted to present, or “play out”, decoded media coming from the decoder606. In the figure, the media play-out unit 608 may represent anyequipment for presenting received media to an end-user. The components602-608 described so far have conventional capabilities, basically, andshould be included in any mobile terminal capable of multimedia.

In order to implement the inventive procedure as described above, thecommunication unit 602 is further adapted to commence mediacommunication in a session with another party using a first RAB. Thefirst RAB may have been obtained for a primary PDP context or for apre-established secondary PDP context, without requesting a new ormodified secondary PDP context specifically adapted for the media to becommunicated, hence a default RAB. Alternatively, the first RAB may havebeen obtained for a regular secondary PDP context based on qualityrequirements of the session, hence a media-adapted RAB.

The mobile terminal 600 further includes a measuring unit 610 adapted tomeasure one or more selected quality-related parameters during saidmedia communication using the first RAB. Quality parameters that themeasuring unit 610 may measure, as indicated by dashed arrows thereto,include a buffer size in data buffer 604, a bitrate in communicationunit 602, an error rate or retransmission rate that may be measuredeither in communication unit 602 or decoder 606, disturbances in themedia play-out or presentation detected from the media play-out unit608, etc. A processor 612 is further arranged in the terminal 600,adapted to receive measurement results from function 610, monitor andevaluate the quality or QoS of communicated media based on saidmeasurements, and to determine whether the quality is acceptable or not,e.g. as described above for stage 4:6 in FIG. 4. The processor 612preferably contains a predetermined monitoring algorithm programmedtherein, to enable said evaluation. The processor 612 is further adaptedto trigger the communication unit 602 to issue a request towards GGSN ina serving access network, for a new or modified secondary PDP contextadapted for the currently communicated media, as soon as the quality ofmedia communication becomes unacceptable according to the predeterminedmonitoring algorithm.

Alternatively or additionally, the quality of the communicated media mayalso be monitored in the network, either by a node located inside theIMS domain as exemplified below or by a node located outside the IMSdomain. In some IMS services, such as Push-to-talk over Cellular (PoC),the media is routed over an IMS node called the “Media Resource FunctionMRF”. In PoC, the combination of the MRF and the SIP application serverbasically make up the PoC Server. The PoC server has knowledge of themedia which it should receive and distribute, as well as it may monitorthe quality of the media it receives and distributes. This knowledgeobtained by the MRF and the application server can be used to trigger anetwork initiated PDP context activation procedure or a networkinitiated PDP context modification procedure.

FIG. 7 is a signalling diagram illustrating different stages in theprocess of initiating and controlling multimedia communication,according to another embodiment. The scenario is similar to the oneshown in FIG. 4, although stages corresponding to 4:1-4:3 are not shownhere, with the difference that the quality is monitored by the networkinstead of, or in addition to, the terminal, and that activation of thesecondary PDP context is initiated by the network. Therefore, a monitorunit 700 is shown here as belonging to the access network 300, althoughit may also reside in the IMS network 306 or in some intermediate node,not shown. The monitor unit 700 may be implemented in a policy node orMRF node or the like. Moreover, the present invention does not excludethat the communication quality can be monitored by both the terminal Aand the monitor unit 700.

A multimedia session is to be established with opposite party 400,either by terminal A calling or contacting party 400, or vice versa. Asin previous examples, a “quick” session establishment stage 7:1 similarto 4:4 may be used, replacing the previous conventional sessionestablishment stage 3:4 and omitting stage 3:5 of selection andactivation of a secondary PDP context at this point. Alternatively, apre-established or regular secondary PDP context may be activated atthis point, as described for previous examples. The description abovefor stage 4:4 applies also to stage 7:4, and will not be repeated againhere.

After establishing the session with the opposite party 400, thecommunication of media is started over the first RAB, as indicated in anext stage 7:2, assuming that the first RAB may be capable of conveyingthe media, at least initially, even though it may not have beenspecifically adapted for the current media. The described procedure mayagain be valid for media transfer in either direction, i.e. to or fromterminal A.

The QoS is now monitored in the background by the monitor unit 700, asindicated by a stage 7:3 a, and optionally also by the mobile terminal Aas indicated in stage 7:3 b during the ongoing media communication ofstage 7:2. Optionally, quality measurement results or the like may alsobe sent from terminal A as feedback to the monitor unit 700 as shown in7:3 c, e.g. using an RTCP protocol, but this is an implementationoption.

The QoS is preferably monitored according to a predetermined monitoringalgorithm, based on requirements derived from the SDP message saved instage 7:1, as well as other factors related to the communicated mediaand the application(s) used. For example, the QoS of a received mediastream may be monitored and evaluated by measuring any of: the number ofpackets in a buffer e.g. in the MRF, the bitrate of the media stream, abit error rate in received packets.

The monitoring algorithm may be configured in several different ways,and may contain various conditions for evaluating the QoS, e.g.depending on the SDP information, although the present invention is notlimited in this respect.

One example may be “PoC version 2” which is a multi-media service thatcan be used to send media bursts containing voice and/or video data toone recipient or plural members of a group. The monitoring algorithm maydetect that the bit rate of the media bursts has increased significantlyby the addition of video bits in the media burst.

If the above measurements generally indicate that the monitored QoSsomehow falls below an acceptable level, a following stage 7:4 ofactivating a secondary PDP context is executed, in order to regainacceptable QoS and a reliable second RAB fulfilling requirements of thecommunicated media. These requirements can be partly derived from theSDP message given during the session establishment stage 7:1, asmentioned above. Stage 7:4 may be initiated as the network A sends arequest PDP context activation to the mobile terminal.

Once the secondary PDP context has been activated or modified and asecond RAB has been allocated that fulfils the specific requirements ofthe communicated media, the session switches to the second RAB in astage 7:5. From now on, the media communication including all mediastreams occurring in the media session, or a sub-set thereof, iscontinued on the second RAB over the media-adapted secondary PDPcontext, in a final illustrated stage 7:6. The session can now be safelycompleted, since the second RAB of the secondary PDP context has beenadapted to the media and application currently used, as in the previousexample of stage 4:9 of FIG. 4.

FIG. 8 is a schematic block diagram illustrating an arrangement in aquality monitor 800 that can be implemented in an access network, amultimedia service network, or in some node outside the multimediaservice network, in accordance with yet another embodiment.

The quality monitor 800 has basically the monitoring function describedabove for block 700 in FIG. 7, and comprises a measurement receiver 802for receiving quality measurements 804 regarding an ongoing multimediasession for a mobile terminal using a first RAB. The qualitymeasurements 804 may be received from an access network, a multimediaservice (e.g. IMS) network, and/or the mobile terminal. Quality monitor800 further comprises a processor 806 for evaluating the qualitymeasurements 804, and for determining whether a media-adapted second RABis needed to fulfil QoS requirements of the ongoing multimedia session.If those requirements are not fulfilled, a PDP context triggering unit808 in the quality monitor 800 sends a message 810 triggering theactivation of a new PDP context, or modification of a usedpre-established or regular secondary PDP context, as described above.The PDP context triggering message 810 may be sent to the mobileterminal or to a GGSN node in the access network, depending on theimplementation.

Using a first RAB, e.g. according to any of the embodiments describedabove, it may not be necessary to delay the communication of media bywaiting for a media-adapted secondary PDP context to be activated and acorresponding second RAB to be allocated. The media communication maythus at least begin over a primary PDP context or pre-establishedsecondary PDP context, and by monitoring and evaluating the quality ofcommunicated media, the quality requirements can be fulfilled byswitching to a second media-adapted RAB, if the quality should becomeunacceptable in relation to the requirements. Thereby, multimediaservices may be more attractive to mobile end-users, and the complexityand general amount of signalling can be reduced for multimedia sessions.Further, the overall occupation of bandwidth and/or radio resources mayalso be reduced.

While the invention has been described with reference to specificexemplary embodiments, the description is in general only intended toillustrate the inventive concept and should not be taken as limiting thescope of the invention. For example, the SIP signalling protocol and IMSconcept have been used throughout when describing the above embodiments,although any other standards and service networks for enablingmultimedia communication may basically be used. The present invention isdefined by the appended claims.

1. A method of establishing a packet-switched multimedia session for amobile terminal connected to a mobile access network for thecommunication of media, comprising the following steps: obtaining afirst Radio Access Bearer RAB, starting the multimedia session bycommunicating said media over the first RAB, monitoring and evaluating aquality of communicated media according to a predetermined monitoringalgorithm, simultaneously with the media communication over the firstRAB, and if the monitored quality is deemed unacceptable according tosaid monitoring algorithm, obtaining a media-adapted second RAB based onquality requirements of the ongoing media communication, and continuingthe media communication over the second RAB.
 2. The method according toclaim 1, wherein the first RAB is obtained by activating a primary PDPcontext adapted for signalling messages.
 3. The method according toclaim 1, wherein the first RAB is obtained by activating apre-established secondary PDP context adapted for media communication.4. The method according to claim 1, wherein the first RAB is a defaultRAB.
 5. The method according to claim 1, wherein the first RAB isinitially adapted for said communicated media.
 6. The method accordingto claim 1, wherein the session is completed over the first RAB, if themonitored quality remains acceptable throughout the session.
 7. Themethod according to claim 1, wherein the media-adapted second RAB isobtained by activating a secondary PDP context adapted for saidcommunicated media.
 8. The method according to claim 3, wherein themedia-adapted second RAB is obtained by modifying said first RAB andpre-established secondary PDP context to be adapted for saidcommunicated media.
 9. The method according to claim 7 or 8, wherein thecommunication of media is switched from the first RAB to themedia-adapted second RAB, once the secondary PDP context has beenactivated or the pre-established secondary PDP context has beenmodified.
 10. The method according to claim 1, wherein saidmedia-adapted second RAB is obtained when at least one media stream hasbeen added or changed during the ongoing media communication.
 11. Themethod according to claim 1, wherein the quality of a received mediastream is monitored by measuring any of the following parameters: apacket buffer size in the terminal, a transfer bit rate, a bit errorrate, a retransmission rate, and detected disturbances in the play-outor presentation of media to an end-user, as input to said monitoringalgorithm.
 12. The method according to claim 11, wherein the monitoringalgorithm is configured such that the monitored quality is deemedacceptable as long as the measured buffer size stays above apredetermined level, and/or if the measured bit rate of the media streamstays above a predetermined level, and/or if the measured bit error rateand/or retransmission rate does not exceed a predetermined level. 13.The method according to claim 12, wherein the monitoring algorithm isconfigured such that the monitored quality is deemed unacceptablewhenever one or more of the measured parameters stays above or does notexceed, respectively, said level(s) for a preset duration or repeatedly.14. The method according to claim 9, wherein SIP is used for signallingand the monitoring algorithm is based on requirements derived frominformation in an SDP message given in an INVITE message, and/or aresponse thereto.
 15. The method according to claim 1, wherein saidquality is monitored and evaluated by the mobile terminal.
 16. Themethod according to claim 1, wherein said quality is monitored andevaluated by a quality monitor in the mobile access network or in amultimedia service network currently controlling the session.
 17. Themethod according to claim 16, wherein said step of obtaining amedia-adapted second RAB is initiated by sending a PDP contexttriggering message to the mobile terminal or to a GGSN node in themobile access network.
 18. An arrangement for establishing apacket-switched multimedia session for a mobile terminal connected to amobile access network for the communication of media, comprising: meansfor obtaining a first Radio Access Bearer RAB, means for starting themultimedia session by communicating said media over the first RAB, meansfor monitoring and evaluating a quality of communicated media accordingto a predetermined monitoring algorithm, simultaneously with the mediacommunication over the first RAB, and means for obtaining amedia-adapted second RAB based on quality requirements of the ongoingmedia communication, if the monitored quality is deemed unacceptableaccording to said monitoring algorithm, such that the session cancontinue over said second RAB.
 19. The arrangement according to claim18, wherein said means for obtaining a first RAB is configured to obtainthe first RAB by activating a primary PDP context adapted for signallingmessages.
 20. The arrangement according to claim 18, wherein said meansfor obtaining a first RAB is configured to obtain the, first RAB byactivating a pre-established secondary PDP context adapted for mediacommunication.
 21. The arrangement according to claim 18, wherein thefirst RAB is a default RAB.
 22. The arrangement according to claim 18,wherein the first RAB is initially adapted for said communicated media.23. The arrangement according to claim 18, further comprising means forcompleting the session over the first RAB, if the monitored qualityremains acceptable throughout the session.
 24. The arrangement accordingto claim 18, wherein said means for obtaining a media-adapted second RABis configured to obtain the second RAE by activating a secondary PDPcontext adapted for said communicated media.
 25. The arrangementaccording to claim 20, wherein said means for obtaining a media-adaptedsecond RAB is configured to obtain the second RAE by modifying saidfirst RAB and pre-established secondary PDP context to be adapted forsaid communicated media.
 26. The arrangement according to claim 25,further comprising means for switching the communicated media from thefirst RAB to the second RAB, once the secondary PDP context has beenactivated or the pre-established secondary PDP context has beenmodified.
 27. The arrangement according to any claim 18, wherein saidmeans for obtaining a media-adapted second RAB is configured to obtain amedia-adapted second RAB when at least one media stream has been addedor changed during the ongoing media communication.
 28. The arrangementaccording to claim 18, wherein the monitoring and evaluating means isconfigured to obtain measurements of any of the following parameters: apacket buffer size in the terminal, a transfer bit rate, a bit errorrate, a retransmission rate, and detected disturbances in the play-outor presentation of media to an end-user, and to provide saidmeasurements to the processor as input to said monitoring algorithm toindicate the quality of a received media stream.
 29. The arrangementaccording to claim 28, wherein the monitoring algorithm is configuredsuch that the quality is deemed acceptable as long as the measuredbuffer size stays above a predetermined level, and/or if the measuredbit rate of the media stream stays above a predetermined level, and/orif the measured bit error rate and/or retransmission rate does notexceed a predetermined level.
 30. The arrangement according to claim 29,wherein the monitoring algorithm is configured such that the monitoredquality is deemed unacceptable whenever one or more of the measuredparameters stays above or does not exceed, respectively, said level(s)for a preset duration or repeatedly.
 31. The arrangement according toclaim 26, wherein SIP is used for signalling and the monitoringalgorithm is based on requirements derived from information in an SDPmessage given in an INVITE message, and/or a response thereto.
 32. Thearrangement according to claim 18, wherein the monitoring and evaluatingmeans is implemented in the mobile terminal.
 33. The arrangementaccording to claim 18, wherein the monitoring and evaluating means isimplemented as a quality monitor in the mobile access network or in amultimedia service network currently controlling the session.
 34. Thearrangement according to claim 33, wherein said means for obtaining amedia-adapted second RAB is configured to send a PDP context triggeringmessage to the mobile terminal or to a GGSN node in the mobile accessnetwork.
 35. An arrangement in a mobile terminal, when connected to amobile access network, for establishing a packet-switched multimediasession for the communication of media, comprising: a communication unitconfigured to obtain a first Radio Access Bearer RAB, and to start themultimedia session by communicating media over the first RAB, and aprocessor configured to monitor and evaluate a quality of communicatedmedia according to a predetermined monitoring algorithm, simultaneouslywith the media communication over the first RAB, and to trigger thecommunication unit to obtain a media-adapted second RAB based on qualityrequirements of the ongoing media communication, if the monitoredquality is deemed unacceptable according to said monitoring algorithm,such that the session can continue over said second RAB.
 36. Thearrangement according to claim 35, further comprising a measuring unitconfigured to provide measurements to the processor from at least oneof: a data buffer, a decoder and a media play-out unit.
 37. A qualitymonitor for monitoring and evaluating a quality of communicated media,comprising:—a measurement receiver for receiving quality measurementsregarding an ongoing multimedia session for a mobile terminal using afirst RAB, a processor for evaluating the quality measurements and fordetermining whether a media-adapted second RAB is needed to fulfillquality requirements of the ongoing multimedia session, and a PDPcontext triggering unit configured to send a message to the mobileterminal or to a GGSN node in the access network, if said quality isdeemed unacceptable according to a predetermined monitoring algorithm,said message triggering a media-adapted second RAB based on qualityrequirements of the ongoing media communication, such that the sessioncan continue over said second RAB.
 38. The quality monitor according toclaim 37, configured to be implemented in a mobile access network towhich the mobile terminal is currently connected, or in a multimediaservice network currently controlling the session.
 39. The qualitymonitor according to claim 37, configured to receive said qualitymeasurements from at least one of: a mobile access network to which themobile terminal is currently connected, a multimedia service networkcurrently controlling the session, and the mobile terminal.
 40. Themethod according to claim 7, wherein said media-adapted second RAB isobtained when at least one media stream has been added or changed duringthe ongoing media communication.
 41. The arrangement according to anyclaim 24, wherein said means for obtaining a media-adapted second RAB isconfigured to obtain a media-adapted second RAB when at least one mediastream has been added or changed during the ongoing media communication.